1. Field of the Invention
The present invention relates to the field of step-up/step-down switching regulators.
2. Prior Art
Step-up/step-down switching regulators use pulse width modulation techniques to control the transfer of energy from a power source to a load. When the voltage ranges of the power source and the load overlap, a common condition in battery powered portable equipment, this control function becomes more complicated. Existing techniques exhibit such undesirable behaviors as frequency subharmonics, increased voltage and current ripple, mode hunting, reduced conversion efficiency and increased component stress. By way of example, an H-bridge circuit such as that shown in FIG. 1 can be used as a buck-boost DC to DC converter. Such a converter and method of operation of such a converter is disclosed in U.S. Pat. No. 6,087,816. This system has a large current ripple. The inductor, capacitors and power switches must be rated at a much larger current than the load current.